1. Field of the Invention
Our present invention relates to an optical process and apparatus for the three-dimensional determination of the shape of objects by means of a calculator.
2. Description of the prior art
Stereoscopy is often used for the determination of the shape of objects by optical means. A first view of the object and a second are taken, the latter being at a different angle from the former, and consideration of these views makes it possible to determine the position of the different points of the surface of the object, when the locations at which the views were taken are known.
In reality, this process is a delicate operation and the difficulty is particularly great when no reference is available, because it is then impossible to compare the images of a single point on to the two views without other information.
In order to resolve this difficulty, it has been proposed to compare areas of the same shape on both images, and to determine the large or small correlation which exists between, on the one hand, the degrees of illumination of the different points of an area of one image and, on the other hand, those of the different points of variously positioned areas of the same shape of the other image, the correlation obviously being at a maximum when the area on the other image corresponds to the same region of the object as the area of the first image.
Usually, the luminosity of each point of an image is made to correspond to a number expressed in a digital system, and the numbers corresponding to a multiplicity of pairs of points are processed in a calculator with a view to studying their correlation.
This processing is long and complicated, all the more so because it is often necessary to distinguish between several maxima of the correlation.
Analog devices exist, particularly optical devices using rotating mirrors, which make it possible to save a certain amount of time in the calculation of the correlation between the degress of illumination of two areas.
However, apart from being delicate to use and adjust, these analog devices do not overcome the problems posed by the digital devices with reference to the local maxima, the displacements of the moving area, and the like, as well as to the dimension and the shape of the areas, which must be small enough to be "quasi-pinpoint" and large enough to contain the information required in order to carry out the correlation.
If processes of this kind have found a use for topographical surveys from the air or by satellite, their application to present-day industrial purposes is difficult to envisage because of the slow operation which restricts their use to static scenes and also because of the high cost of the calculations involved.
It has also been tried, with a view to a more practical use of the stereoscopy process, to mark the surface of the object whose shape is to be explored. This marking is time-consuming and expensive as well as complicated, and cannot always be used.
Furthermore, the known installations of this type use, in order to take views of the object under observation, two cameras provided with a conventional sweep system, the volume of data provided by the cameras resulting in a long treatment time. These installations are also limited to the representation of a contour line of the surface of the object.
Another installation, which is able to compute a profile line of an object, is known from the German Offenlegungschrift No. 2,113,522, which describes the use of the reflection over the surface of the object of a laser pencil having a variable inclination in a given plane, the reflected pencil being intercepted by a receiving device. The determination of the profile line necessitates the computation of the inclination of the emitted and received pencils with respect to a straight reference line, together with the knowledge of the position of both the laser emitter and the receiving device.
This type of installation is limited both in its object and in its use.